IR light is longer in wavelength than visible light and focuses differently and we need to adjust this focus manually. In fact, an infrared photography is almost never sharp. It is an utopia. To realize a photography strictly sharp is exceptional or even impossible. Moreover, the photocamera lenses are not designed for the IR light, that is why they tend to show much stronger dispersion in the near-IR, which in turn leads to CA and blurring. Even the focus adjustment would not help.